This invention relates to reclaiming waste plastics and more particularly to process and product improvements applicable to such reclamation.
As set forth, for example, in United States Bureau Of Mines Report Of Investigations 7955, entitled "Recycling Of Plastics From Urban And Industrial Refuse", 1974, it is known to reclaim waste plastics for refabrication into similar or different products, or for pyrolysis to recover monomers forming the thermoplastic materials, or for incineration where the plastics serve as a high-energy fuel source.
Molecularly oriented articles such as sheet, film, bags, containers in the form of trays, bottles, cups and the like have been increasingly appearing in the marketplace and represent candidates for reclamation. Such orientation is employed to improve strength, thereby facilitating a reduction in the plastic used over that necessary in non-molecularly oriented articles of equal strength. Generally, such orientation involves stretching the thermoplastic material while within a pre-selected temperature range in plural (usually two) directions during fabrication in order to orderly align the molecules in the direction of stretch, followed by quenching while under stress to lock in the orientation. One category of molecularly oriented articles having major, though not exclusive, application in food and beverage packaging are containers such as bottles, formed of high barrier thermoplastic materials, i.e., those having respective oxygen and carbon dioxide permeabilities of less than 20 and 30 cc./day/100 sq.in./mil./atm. at 73.degree. F., and it is especially desirable to recover such containers in view of the rather expensive nature of these high barrier materials.
In general, reclaiming usually involves grinding the waste articles to reduce size, segregating the various types of different materials from each other before or after such grinding, optionally followed by washing prior to either recycling for refabrication, or pyrolysis for monomer recovery, or incineration for energy recovery. When the collected articles are labeled, as is frequently the case with packaged products, the labels must be separated in the recovery process, usually during washing, in order to avoid contamination of the purified resin. Label removal can present problems, usually because of the rather tenacious adherence of the label material to the article surface via adhesives which do not readily dissolve or may even be completely insoluble in conventional liquids otherwise suitable for washing the plastics.